This error occurs when the maximum hop count exceeds. The hop count is the number of mail servers the email message passes through to reach its destination (recipient). The hop count may increase when specific mail servers trigger various redirections. Ultimately these redirections may cause the hop count to exceed the maximum and will not send the email as the sender's SMTP server could not figure out the destination.
Additionally, you may encounter this error in Office 365 if there are one or more unverified domains.
Sometimes, you may have a complex organizational structure and require your email to route through different servers before it reaches the internet. In such scenarios, consider increasing the maximum hop count. However, note that the hop count can only be between 10 and 256.
On the other hand, if you are running Office 365 as your SMTP client, ensure that all the mail domains are verified.
Finally, if nothing works, contact the SMTP provider to obtain more information on what can cause the hop count to exceed.
View all errors